A PC-program performing the Potthoff-Roy (PR) multigroup (G-sample) analysis of longitudinal data is described and illustrated.

This program and the underlying statistical model are useful in the comparison of several longitudinal samples.

Applications include the study of growth, development, adaptation, aging, and treatment effects (in short, any phenomenon in whi2c1h the passage of time is important) for which serial data are available.

Specifically, this method fits polynomials to the average growth curves in the samples, and tests hypotheses concerning the curves themselves and the individual coefficients of the polynomials.

The program features the utilization of orthogonal polynomial regression coefficients 2(OPRCs) and is written in GAUSS, a relatively inexpensive yet comprehensive matrix programming language.